For the purposes of the present invention, fuel dusts are finely milled coals having different degrees of carbonization, dusts composed of biomasses, products of thermal pretreatment, e.g. coke, dried products obtained by “torrefaction” and also calorific fractions from domestic and industrial residues and wastes. The fuel dusts can be fed as a gas-solid or liquid-solid suspension to the gasification. The gasification reactors can be provided with a cooling shield or with a refractory lining, as disclosed in the patents DE 4446803 and EP 0677567. In various systems which have been introduced into industry, crude gas and the molten slag can be discharged separately or together from the reaction space of the gasification apparatus, as described in DE 19718131.
Owing to the fuel particles which have been milled to dust fineness and short reaction times in the gasification space, entrained flow gasification results in an increased proportion of dust in the crude gas. This fly dust consists, depending on the reactivity of the fuel, of soot, and reacted fuel particles and also fine slag and ash particles. The size varies from coarse particles having diameters of greater than 0.5 mm to fine particles having a diameter of up to 0.1 The ease with which the particles can be separated from the crude gas is dependent on this diameter but also on the composition of the particles. A distinction can basically be made between soot and ash or slag particles, with soot particles generally being smaller and more difficult to separate from the crude gas. Slag particles have a higher density and are thus easier to separate off, but have a greater hardness and erosive effect. This leads to increased wear in the lines conveying the crude gas and can result in safety-relevant leaks and decreases in the life of these plant components. Various scrubbing systems are used for removing the dusts resulting from the fuels.
Prior art is summarized in the patent document DE 10 2005 041 930 and in “Die Veredelung and Umwandlung von Kohle” DGMK, Hamburg, December 2008, Schingnitz, chapter “GSP-Verfahren”. According to this, the crude gasification gas together with the slag formed from the fuel ash leaves the gasification space at temperatures of 1200-1900° C. and is cooled in a downstream quenching space by spraying in excess water and is freed of the slag and to a small extent of entrained dust, with the quenching space being able to be configured as a free-space quencher or be equipped with a central tube conveying crude gas. A free-space quenching system is disclosed, for example, in DE 10 2007 042543, in which the crude gas leaving the gasification space is sprayed with water and taken off in the lower part under a roof construction. DE 10 2006 031816 discloses a free quenching space completely without internals, with quenching water being injected at one or more levels in such an amount that the crude gas is cooled and saturated with water vapor and the excess quenching water is taken off either alone or together with precipitated slag in the lower part. Variants having a central tube are disclosed in the patent DE 199 52 754, in which the central tube is configured in the form of a Venturi tube, DD 145860, in which the crude gas is subjected to an additional scrub in the form of an airlift pump, and DD 265051, in which elements for distributing the exiting crude gas at the end of the central tube are supposed to ensure uniform outflow. CN 101003754-B describes an immersion quenching apparatus having a central tube in which the hot crude gas from the gasification reactor is conveyed together with the likewise hot slag downward into water beneath the surface thereof and flows upward as gas-water suspension in the annular gap of the guide tube configured as a double tube. Gas-water separation occurs at the upper end of the guide tube. The gas-water suspension flowing upward in the annular gap is said to protect the inner central tube against overheating.
The solution to the problem proposed in the patent DE 10 2007 042 543 has the disadvantage that the free space through pipes having a relatively large diameter for discharging the crude gas and the roof construction provides deposition surfaces for entrained slags and dusts, which experience has shown leads to blockages. DE 10 2006 031816 requires uniform outflow of the hot crude gas from the gasification space because otherwise there could be a risk of thermal overloading of the pressure-rated vessel walls. The installation of a Venturi tube as described in DE 199 52 754 can lead to undesirable pressure fluctuations in the gasification space which are difficult to equalize by regulation technology because of their brief duration. Internals in the quenching and scrubbing space, as described in the patents DD 265051 and DD 145860, can lead to cement-like products due to the pozzolanic properties of, in particular, the fine dust components in the case of particular types of coal and ash and these likewise lead to blockages and an increase in the pressure drop. This risk is likewise present in the case of the problem solution proposed in CN 101003754-B. The gap between the inner and outer tubes of the central tube can become blocked, and the hot crude gas flowing downward in the uncooled inner tube can lead to thermal destruction of the inner tube and additionally endangers the pressure wall of the quenching space by overheating.